MRI compatible electrode circuit

ABSTRACT

An MRI compatible electrode circuit construct is provided. The construct includes at least two filter components constructed from an electrode wire. One filter component may be a resonant LC filter at or near an electrode/wire interface that resolves the issue of insufficient attenuation by effectively blocking the RF induced current on the wire from exiting the wire through the electrode. The second filter component may include one or more non-resonant filter(s) positioned along the length of the electrode wire that resolve(s) the issue of excessive heating of the resonant LC filter by significantly attenuating the current induced on the wire before it reaches the resonant LC filter. The non-resonant filter(s) may also attenuate the RF current reflected from the resonant LC filter thereby resolving the issue of the strong reflected power from the resonant filter and the associated dielectric heating.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/743,954, which is a national stage entry application ofSerial No.: PCT/US2010/026232, filed on Mar. 4, 2010, which claimspriority to provisional application U.S. Ser. No. 61/157,482, filed onMar. 4, 2009, the entireties of which are herein incorporated byreference.

The invention relates to medical devices with tissue contactingelectrodes used in the magnetic resonance imaging (MRI) environment andin particular to a method and device for attenuating electromagneticfields applied to such devices during MRI scanning.

BACKGROUND OF THE INVENTION

MRI has achieved prominence as a diagnostic imaging modality, andincreasingly as an interventional imaging modality. The primary benefitsof MRI over other imaging modalities, such as X-ray, include superiorsoft tissue imaging and avoiding patient exposure to ionizing radiationproduced by X-rays. MRI's superior soft tissue imaging capabilities haveoffered great clinical benefit with respect to diagnostic imaging.Similarly, interventional procedures, which have traditionally usedX-ray imaging for guidance, stand to benefit greatly from MRI's softtissue imaging capabilities. In addition, the significant patientexposure to ionizing radiation associated with traditional X-ray guidedinterventional procedures is eliminated with MRI guidance.

MRI uses three fields to image patient anatomy: a large static magneticfield, a time-varying magnetic gradient field, and a radiofrequency (RF)electromagnetic field. The static magnetic field and time-varyingmagnetic gradient field work in concert to establish proton alignmentwith the static magnetic field and also spatially dependent proton spinfrequencies (resonant frequencies) within the patient. The RF field,applied at the resonance frequencies, disturbs the initial alignment,such that when the protons relax back to their initial alignment, the RFemitted from the relaxation event may be detected and processed tocreate an image.

Each of the three fields associated with MRI presents safety risks topatients when a medical device is in close proximity to or in contacteither externally or internally with patient tissue. One importantsafety risk is the heating that can result from an interaction betweenthe RF field of the MRI scanner and the medical device (RF-inducedheating), especially medical devices which have elongated conductivestructures with tissue contacting electrodes, such as electrode wires inpacemaker and implantable cardioverter defibrillator (ICD) leads,guidewires, and catheters. Thus, as more patients are fitted withimplantable medical devices, and as use of MRI diagnostic imagingcontinues to be prevalent and grow, the need for safe devices in the MRIenvironment increases.

A variety of MRI techniques are being developed as alternatives to X-rayimaging for guiding interventional procedures. For example, as a medicaldevice is advanced through the patient's body during an interventionalprocedure, its progress may be tracked so that the device can bedelivered properly to a target site. Once delivered to the target site,the device and patient tissue can be monitored to improve therapydelivery. Thus, tracking the position of medical devices is useful ininterventional procedures. Exemplary interventional procedures include,for example, cardiac electrophysiology procedures including diagnosticprocedures for diagnosing arrhythmias and ablation procedures such asatrial fibrillation ablation, ventricular tachycardia ablation, atrialflutter ablation, Wolfe Parkinson White Syndrome ablation, AV nodeablation, SVT ablations and the like. Tracking the position of medicaldevices using MRI is also useful in oncological procedures such asbreast, liver and prostate tumor ablations; and urological proceduressuch as uterine fibroid and enlarged prostate ablations.

The RF-induced heating safety risk associated with electrode wires inthe MRI environment results from a coupling between the RF field and theelectrode wire. In this case several heating related conditions exist.One condition exists because the electrode wire electrically contactstissue through the electrode. RF currents induced in the electrode wiremay be delivered through the electrode into the tissue, resulting in ahigh current density in the tissue and associated Joule or Ohmic tissueheating. Also, RF induced currents in the electrode wire may result inincreased local specific absorption of RF energy in nearby tissue, thusincreasing the tissue's temperature. The foregoing phenomenon isreferred to as dielectric heating. Dielectric heating may occur even ifthe electrode wire does not electrically contact tissue, such as if theelectrode was insulated from tissue or if no electrode was present. Inaddition, RF induced currents in the electrode wire may cause Ohmicheating in the electrode wire, itself, and the resultant heat maytransfer to the patient. In such cases, it is important to attempt toboth reduce the RF induced current present in the electrode wire and tolimit the current delivered into the surrounding tissue.

Methods and devices for attempting to solve the foregoing problem areknown. For example, high impedance electrode wires limit the flow ofcurrent and reduce RF induced current; a resonant LC filter placed atthe wire/electrode interface may reduce the current delivered into thebody through the electrodes, non-resonant components placed at thewire/electrode interface may also reduce the current transmitted intothe body; and co-radial electrodes wires may be used to provide adistributed reactance along the length of the wire thus increasing theimpedance of the wire and reducing the amount of induced current.

Notwithstanding the foregoing attempts to reduce RF-induced heating,significant issues remain. For example, high impedance electrode wireslimit the functionality of the electrode wire and do not allow foreffective ablation, pacing or sensing. Resonant LC filters placed at thewire/electrode interface inherently result in large current intensitieswithin the resonant components resulting in heating of the filteritself, at times exceeding 200.degree. C. Additionally, a resonant LCfilter at the wire/electrode interface can result in a strong reflectionof the current induced on the electrode wire and may result in astanding wave that increases the temperature rise of the wire itselfand/or results in increased dielectric heating near the electrode wirewhich in turn heats surrounding tissue to potentially unacceptablelevels and may melt the catheter or lead body in which it is housed.Non-resonant components alone do not provide sufficient attenuation toreduce the induced current to safe levels. Additionally, the componentswill experience a temperature rise, if the conductor cross-sectionalarea is too small. While an electrode wire with distributed reactance(i.e. coiled wires) can reduce the level of induced current on the wire,it does not sufficiently block the current that is induced on the wirefrom exiting the wire through the electrodes. Thus, while coiled wiresmay work for certain short lengths or distances, in situations requiringlonger lengths or distances, coiled wires do not by themselves provideenough impedance to block current.

Current technologies for reducing RE-induced heating in medical devices,especially those with elongated conductive structures such as electrodewires, are inadequate. Therefore, new electrode wire constructs and leador catheter assemblies are necessary to overcome the problems ofinsufficient attenuation of RF energy.

BRIEF SUMMARY OF THE INVENTION

It is an object of the invention to provide an improved device andmethod for reducing RF-induced heating of tissue by attenuating the RFcurrent induced in the medical device by MRI.

It is a further object of the invention to provide a novel circuitconstruction that is MRI compatible and resolves the limitations of thecurrent technology such as insufficient attenuation of RF energy.

It is a further object of the invention to provide a novel circuitconstruction that maintains physical flexibility, maneuverability andthe ability to bend.

In one embodiment the invention is a circuit adapted to be used with animplantable or interventional lead or catheter assembly. Each circuitincludes a plurality of filter components constructed from a singlewire.

In one embodiment the filter component comprises two filter components.One filter component may be a resonant filter at or near theelectrode/wire interface that resolves the issue of insufficientattenuation by effectively blocking the RF induced current on the wirefrom exiting the wire through the electrode. The second filter componentmay comprise one or more non-resonant filter(s) or inductors positionedalong the length of the wire that resolve(s) the issue of excessiveheating of the resonant LC filter by significantly attenuating thecurrent induced on the wire before it reaches the resonant LC filter.The non-resonant filters(s) may also attenuate the RF current reflectedfrom the resonant LC filter thereby resolving the issue of the strongreflected power from the resonant filter and the associated dielectricheating.

In one embodiment, the non-resonant filters may comprise a plurality ofmultiple inductors placed in close proximity such as withinapproximately 1 cm or less for the purpose of providing more attenuationthan a single filter alone, while still allowing the device to bend.

In one embodiment, multiple non-resonant filters placed in closeproximity may be formed to create a distributed reactance. For example,two co-radially wound electrode wires may create a distributedreactance. In an alternative embodiment three or more co-radially woundelectrode wires may include create a distributed reactance. A furtheralternative embodiment may include the use of two or more coaxiallywound wires for the electrodes.

In one embodiment, the novel electrode circuit construct may include asingle wire thereby eliminating the need for bonding points whichreduces the possibility of mechanical failure of the wire.

In one embodiment an electrode wire has a cross sectional area such thatthe resistivity of the wire at the MR operating frequency, 64 MHz for a1.5 T MRI for example, is low enough to ensure that heating of the wireis minimal.

In one embodiment the electrode circuit and integrated components may beconstructed to be integrated into a 10 French or smaller catheter.

In one embodiment the electrode circuit may be used in an implantedmedical device such as ICDs, pacemakers, neurostimulators, and the like.

In one embodiment a catheter or lead assembly includes an elongated bodyhaving first and second ends. The elongate body defines a lumentherewithin which receives first and second circuits. First and secondcircuits each include an electrode wire that forms a plurality offilters distributed along a length thereof. A tip electrode located atthe distal end of the elongate body is coupled to the second electrodewire. The elongate body also includes a ring electrode at the first endand proximal to the tip electrode. The ring electrode is electricallycoupled to the first wire. The second end of the elongate body isoperably coupled to electronic controls, either external or internal tothe body. In one embodiment, the second end attaches to amplifiers forsensing cardiac activity, as well as a pacing circuit to stimulatecardiac tissue. The second end may also be connected to an RF ablationgenerator to ablate, for example, cardiac tissue. One filter formed byeach electrode wire may be a resonant LC filter at or near theelectrode/wire interface that resolves the issue of insufficientattenuation by effectively blocking the RF induced current on the wirefrom exiting the wire through the electrode. A second filter formed byeach electrode wire may comprise one or more non-resonant filter(s) orinductors positioned along the length of the elongate body thatresolve(s) the issue of excessive heating of the resonant LC filter byattenuating the current induced on the wire before it reaches theresonant LC filter. The non-resonant filter(s) may also attenuate the RFcurrent reflected from the resonant LC filter thereby resolving theissue of the strong reflected power from the resonant filter and theassociated dielectric heating.

In another embodiment a lead assembly includes an elongated body havingfirst and second ends. A plurality of electrodes is located at thedistal end of the elongate body. The plurality of electrodes may includea tip electrode and any number of ring electrodes or may comprise aplurality of ring electrodes. The elongate body further defines a lumentherewithin which receives a plurality of circuits. Each individualelectrode wire comprising the plurality of circuits forms a plurality ofnon-resonant filters, or inductors, distributed along a length thereof.The second end of the elongate body may be operably coupled toelectronic controls, either external or internal to the body, amplifiersfor sensing cardiac activity, a RF ablation generator, and/or the like.Each individual circuit comprising the plurality of electrode wires alsoforms a resonant LC filter positioned within the lumen of the elongatebody at a distal end thereof at or near the electrode/wire interface.

In another embodiment a lead assembly includes an elongate body having aproximal end and a distal end, the elongate body defining a lumentherewithin. The distal end is arranged and configured to contact tissueand the proximal end is operably coupled to an electronic control. Atleast one electrode is located on the elongate body and at least oneelectrical circuit is in communication with the at least one electrode.The circuit is housed within the elongate body and includes one or moreelectrode wires that form at least one non-resonant filter and at leastone resonant LC filter. The resonant LC filter is positioned at thedistal end of the elongate body proximate an electrode/wire interface.The circuit may be flexible or rigid.

Other aspects of the invention are encompassed by the following clauses.

1. A lead assembly comprising:

an elongate body having a proximal end and a distal end, said elongatebody defining a lumen therewithin, the distal end arranged andconfigured to contact tissue and the proximal end operably coupled to anelectronic control;

a plurality of electrodes located on the elongate body; and

a plurality of electrode circuits each of which is in communication witha respective one of said plurality of electrodes, said plurality ofelectrode circuits housed within said elongate body and each comprisingone or more electrode wires, said one or more electrode wires formingone or more non-resonant filters and one or more resonant LC filters.2. The lead assembly of clause 1 wherein said one or more electrodewires each comprise a single continuous length of electrode wire.3. The lead assembly of clause 2 wherein said one or more non-resonantfilters comprise a single non-resonant filter positioned along a portionof the length of the electrode circuit.4. The lead assembly of clause 1 wherein said one or more non-resonantfilters comprise a plurality of non-resonant filters positioned in auniform or non-uniform spaced-apart relationship along a portion of thelength of the electrode circuit.5. The lead assembly of clause 1 wherein said at least one non-resonantfilter is constructed from a length of electrode wire that is notcontinuous with a length of electrode wire used to construct said atleast one resonant LC filter.6. The lead assembly of clause 1 wherein said one or more electrodewires comprises a single length of multiple non-continuous wires.7. The lead assembly of clause 1 wherein said one or more non-resonantfilters in a single electrode circuit comprises a plurality ofnon-resonant filters positioned in a non-spaced apart relationship withno gaps therebetween along a portion of the length of the electrodecircuit.8. The lead assembly of clause 1 wherein said one or more non-resonantfilters comprise a plurality of non-resonant filters positioned in aco-axial relationship.9. The lead assembly of clause 1 wherein said one or more resonant LCfilters comprise a plurality of resonant LC filters positioned in aco-axial relationship.10. The lead assembly of clause 1 wherein said plurality of electrodecircuits share the same longitudinal axis along at least a portionthereof.11. The lead assembly of clause 10 wherein said plurality of electrodecircuits share the same longitudinal axis in a parallel relationship toeach other along at least a portion thereof.12. The lead assembly of clause 1 wherein said plurality of electrodecircuits are positioned along different axes of the elongate body.13. The lead assembly of clause 1 wherein said plurality of electrodecircuits share a common axis along at least a portion thereof but havedifferent inner diameters.14. The lead assembly of clause 1 wherein said one or more electrodewires comprise copper, titanium, titanium alloys, tungsten, gold,multifilar and combinations of the foregoing.15. The lead assembly of clause 1 wherein one or more electrode wiresincludes an insulative coating bondable by heat, chemical or adhesivemeans.16. The lead assembly of clause 1 wherein said plurality of electrodesare positioned in a parallel relationship on either side of saidelongate body.17. The lead assembly of clause 1 wherein said electrode circuit ishoused entirely within the lumen of said elongate body.18. The lead assembly of clause 1 further comprising a flexible tubearound which said at least one non-resonant and resonant LC filters arehelically wound.19. The lead assembly of clause 1 wherein said one or more resonant LCfilters comprise a plurality of physically stacked layers.20. The lead assembly of clause 19 wherein said physically stackedlayers comprise an inner layer, a middle layer and an outer layer.21. The lead assembly of clause 20 wherein said inner layer, middlelayer and outer layer are formed from said one or more electrode wiresin a ratio of turns of approximately 3:2:1.22. The lead assembly of clause 21 wherein said inner layer isconstructed of approximately 30 turns, said middle layer is constructedof approximately 20 turns, and said outer layer is constructed ofapproximately 10 turns of said one or more electrode wires.23. The lead assembly of clause 1 wherein said one or more non-resonantfilters are configured to create at least 1,000 or more Ohms ofimpedance along said electrode circuit for each one meter of leadassembly length.24. The lead assembly of clause 1 wherein the circuit is flexible.25. The lead assembly of clause 1 wherein the circuit is rigid.26. The lead assembly of clause 1 wherein said one or more non-resonantfilters and said one or more resonant LC filters comprise discretefilters structured to be joined by multiple connecting segments ofelectrode wire.27. The lead assembly of clause 4 wherein said uniform spacing comprisesrepetitious spacing.28. A lead assembly comprising:an elongate body having a proximal end and a distal end, said elongatebody defining a lumen therewithin, the distal end arranged andconfigured to contact tissue and the proximal end operably coupled to anelectronic control;one or more electrodes located on the elongate body; andone or more electrical circuits each of which is in communication with arespective said one or more electrodes, each of said one or morecircuits housed within said elongate body and comprising one or moreelectrode wires, said one or more electrode wires forming at least onenon-resonant filter having a substantially uniformly distributedinductance along the length of said electrode wire and at least oneresonant LC filter.29. The lead assembly of clause 28 wherein said at least onenon-resonant filter comprises a plurality of non-resonant filterspositioned in a spaced apart relationship along a length of saidelectrical circuit.30. The lead assembly of clause 29 wherein said spaced apartrelationship is repetitious.31. The lead assembly of clause 29 wherein said spaced apartrelationship is uniform.32. The lead assembly of clause 28 wherein said one or more wires eachcomprise a single, continuous length of electrode wire forming said atleast one non-resonant filter and said at least one resonant LC filter.33. The lead assembly of clause 28 wherein said one or more non-resonantfilters comprise a single non-resonant filter positioned along a portionof the length of the electrode circuit.34. The lead assembly of clause 28 wherein said at least onenon-resonant filter is constructed from a length of electrode wire thatis not continuous with a length of electrode wire used to construct saidat least one resonant LC filter.35. The lead assembly of clause 28 wherein said one or more electrodewires comprises a single length of multiple non-continuous wires.36. The lead assembly of clause 28 wherein said one or more non-resonantfilters in a single electrode circuit comprises a plurality ofnon-resonant filters positioned in a non-spaced apart relationship withno gaps therebetween along a portion of the length of the electrodecircuit.37. The lead assembly of clause 28 wherein said at least onenon-resonant filter comprises a plurality of non-resonant filterspositioned in a co-axial relationship.38. The lead assembly of clause 28 wherein said at least one resonant LCfilter comprises a plurality of resonant LC filters positioned in aco-axial relationship.39. The lead assembly of clause 28 wherein said one or more electricalcircuits comprise a plurality of electrode circuits that share the samelongitudinal axis along at least a portion thereof.40. The lead assembly of clause 39 wherein said plurality of electricalcircuits share the same longitudinal axis in a parallel relationship toeach other along at least a portion thereof.41. The lead assembly of clause 28 wherein said one or more electricalcircuits comprise a plurality of electrical circuits positioned alongdifferent axes of the elongate body.42. The lead assembly of clause 28 wherein said one or more electricalcircuits comprise a plurality of electrical circuits share a common axisalong at least a portion thereof but have different inner diameters.43. The lead assembly of clause 1 wherein said one or more electrodewires comprise copper, titanium, titanium alloys, tungsten, gold,multifilar and combinations of the foregoing.44. The lead assembly of clause 28 wherein said one or more electrodewires include an insulative coating bondable by heat, chemical oradhesive means.45. The lead assembly of clause 28 wherein said one or more electrodesare positioned in a parallel relationship on either side of saidelongate body.46. The lead assembly of clause 1 wherein said one or more electricalcircuits are housed entirely within the lumen of said elongate body.47. The lead assembly of clause 28 further comprising a flexible tubearound which said at least one non-resonant and resonant LC filters arehelically wound.48. The lead assembly of clause 28 wherein said one or more resonant LCfilters comprise a plurality of physically stacked layers.49. The lead assembly of clause 28 wherein one or more of saidelectrical circuits are flexible.50. The lead assembly of clause 28 wherein one or more of saidelectrical circuits are rigid.51. The lead assembly of clause 28 wherein said at least onenon-resonant filter and said at least one resonant LC filters comprisediscrete filters structured to be joined by multiple connecting segmentsof electrode wire.

While multiple embodiments, objects, feature and advantages aredisclosed, still other embodiments of the invention will become apparentto those skilled in the art from the following detailed descriptiontaken together with the accompanying figures, the foregoing beingillustrative and not restrictive.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram depicting the basic components of theinvention housed within a catheter or lead assembly.

FIG. 2 is a diagram depicting an embodiment of the invention in whichnon-resonant filters are distributed along a wire in a spaced apartrelationship with a resonant LC filter proximate an electrode.

FIG. 3A is a sectional view of an exemplary medical device including MRcompatible conductive electrode wires forming non-resonant filtersdistributed along the wire and each wire forming a resonant LC filterproximate an electrode.

FIG. 3B is a sectional view of an exemplary medical device including MRcompatible conductive electrode wires in which non-resonant filters areformed without any gaps therebetween and in which one electrode circuitis wound on top of or over a second electrode circuit.

FIG. 3C is a sectional view of an exemplary medical device including MRcompatible conductive electrode wires in which one resonant LC filter iswound on top of or over a second resonant LC filter.

FIG. 3D is a sectional view of an exemplary medical device including aplurality of circuits in which the non-resonant section comprises onnon-resonant filter.

FIG. 3E shows a detailed view of the resonant LC filters andnon-resonant filters of FIG. 3A.

FIG. 4A is a schematic view of the exemplary medical device of FIG. 3with MR compatible electrode wires positioned within the lumen of thelead assembly.

FIG. 4B is a schematic view of an exemplary medical device with MRcompatible electrode wires embedded in a jacket surrounding the leadassembly.

FIG. 5 depicts an embodiment of the invention in which multiplenon-resonant inductors formed from a single wire are grouped togetherand distributed along the wire and further forming a resonant LC filterproximate an electrode.

FIG. 6A is a perspective view depicting co-radially wound electrodewires.

FIG. 6B is a schematic view of the co-radially wound wires of FIG. 6Apositioned inside an exemplary medical device with resonant LC filtersproximate electrodes.

FIG. 6C is a schematic view of the co-radially wound wires of FIG. 6Aembedded in the jacket of the exemplary medical device with resonant LCfilters proximate electrodes.

DETAILED DESCRIPTION OF THE INVENTION

In describing the invention herein, reference is made to an exemplarylead assembly comprising a catheter. However, as will be appreciated bythose skilled in the art the present invention may be used with anyimplantable medical device. By implantable we mean permanently as withcardiac pacemakers, defibrillators and neurostimulators; or temporarilyimplantable such as in interventional procedures and including by way ofexample cardiac ablation devices and the like. Further the exemplarylead assembly may be used external to the body but still be in contactwith body tissue such as the skin. Also as used herein, an electrodewire is any conductive structure that is in electrical contact with anelectrode. Typically, an electrode wire is an actual wire; however, anelectrode wire may also be a circuit board trace, a conductive lumen, orany material which conducts electricity.

FIG. 1 is a block diagram illustrating the lead assembly 100 in itssimplest form in accordance with the present invention. Lead assembly100 broadly includes elongate body 110 having first 112 and second 114ends and defining a lumen 116 therewithin. Electrode 118 is located atthe first end 112 of elongate body 110 and is in electricalcommunication with circuit 120. Lumen 116 houses circuit 120. Circuit120 includes at least one electrode wire 122 forming a plurality ofspaced apart filter components 124. Each circuit 120 may be constructedfrom a single, continuous length of wire. Alternatively, the circuit 120may be constructed with discrete filter components and a singleelectrode wire or multiple lengths of non-continuous electrode wireconnecting the discrete filter components. Alternatively, the circuit120 may be constructed with one electrode wire forming filter components124 and a discrete electrode wire forming filter component 126. Anynon-magnetic wire may be used in constructing the circuit in accordancewith the present invention, including copper, titanium, titanium alloys,tungsten, gold and combinations of the foregoing. Optionally, electrodewire 120 is a bondable wire such as heat, chemical or adhesivelybondable to permit formation of the filters during manufacture with onewire. In the case in which multiple lengths of wire are used asconnecting segments, the wires may be cast in silicone and/orheat-treated along the length at certain points to ensure that the wiredoes not shift. Alternatively, any wire that is sufficiently rigid sothat it holds its shape when bent may be used. Electrode wire 120 mayalso form filter component 126 positioned adjacent the wire/electrodeinterface 128 to effectively block RF induced current from exiting thelead assembly through the electrode 118. Additional filtering components124 distributed along the length of the wire attenuate the inducedcurrent on the wire itself before the current reaches filter component126 thereby avoiding excessive heating of filter component 126.Excessive heating will occur when the temperature of the filter risesapproximately 2 to 4 degrees above the normal temperature of the tissuethat the device contacts.

Preferably, filter component 126 at the electrode/wire interface 128 isa resonant LC filter that resolves the problem of insufficientattenuation by effectively blocking the RF induced current on wire 122.Filter components 124 preferably include a plurality of non-resonantfilters or inductors that address excessive heating of the resonant LCfilter by significantly attenuating the current induced on the wirebefore the current reaches the resonant LC filter. Non-resonant filtercomponents 124 may also attenuate the RF current reflected from resonantLC filter component 126 thereby attenuating the strong reflected powerfrom the resonant LC filter 126 and reducing the associated dielectricheating.

FIG. 2 is a schematic diagram depicting an embodiment of the invention.Lead assembly 200 broadly includes an elongate body 210 having first 212and second 214 ends and includes lumen 216 therewithin. Lead or catheterassembly 200 includes first electrode 218 located at the first end 212of lead assembly 200. First electrode 218 may be a tip electrode.Alternatively, first electrode may be a ring electrode or otherelectrodes known to those skilled in the art. Lumen 216 houses circuit220. Circuit 220 includes at least one conductive electrode wire 222forming a plurality of spaced apart filter components 224. Each circuitmay constructed from a single, continuous length of non-magnetic wiresuch as copper, titanium, titanium alloys, tungsten, gold andcombinations of the foregoing. Alternatively, each circuit may comprisemultiple lengths of wires. As with the embodiment depicted in FIG. 1,electrode wire 222 is a bondable wire such as heat, chemical oradhesively bondable to permit formation of the filters duringmanufacture with one wire. This eliminates the necessity for connectionpoints at each end of each filter 224 and thereby improving themechanical durability of the circuit 220 and reducing the manufacturingcost thereof. In the illustrated embodiment, the lead assembly 200includes resonant LC filter 226 positioned adjacent and proximal to thewire/electrode interface 228. Resonant LC filter assembly 226 is adaptedto effectively block RF induced current from exiting the lead assembly200 through the electrode 218. Resonant LC filter 226 effectively blocksRF induced current by being constructed such that the inductive andcapacitive characteristics of the filter together resonate to create ahigh impedance at the MRI RF frequency of interest for example,approximately 64 MHz for a 1.5 Tesla MRI or approximately 128 MHz for a3.0 Tesla MRI. Filtering components 224 distributed along the length ofthe wire attenuate the induced current on the wire itself before thecurrent reaches resonant LC filter 226 thereby avoiding excessiveheating of resonant LC filter 226. The filtering components 224 togetherpreferentially create at least 1,000 or more Ohms of impedance along theentire circuit 220, for a lead length of approximately 1 meter. Those ofskill in the art will appreciate that the amount of total impedance willnecessarily change as the lead length varies. Each filtering component224 may comprise an inductor formed by electrode wire 222 withapproximately 45 turns, creating approximately 150 Ohms, when sized tofit in an 8 French catheter assuming an inside diameter of the inductorto be 0.045 inches. Fewer turns are necessary to create the sameimpedance for larger diameter inductors. Filtering components 224 may bespaced non-uniformly, such that the segments of wire between them eachhave a different resonant frequency, or substantially uniformly.

Referring now to FIG. 3A a detailed sectional view of one embodiment ofthe invention is illustrated. Lead assembly 300 includes elongate body310 surrounded by jacket 311. Elongate body 310 includes first 312 andsecond 314 ends and includes lumen 316 therewithin. Second end 314 isadapted to be connected to electronic controls, internal or external tothe patient body, and may include a connector (not shown). Lumen 316houses circuits 320, 321. Circuits 320, 321 each include one conductiveelectrode wire 322, 323, respectively, located within the lumen 316 oflead assembly 300. In an alternative embodiment, conductive electrodewires 322, 323 can be embedded in jacket 311, as seen in FIG. 4B,thereby decreasing the overall diameter of the lead assembly 300. Eachconductive electrode wire 322, 323 comprises a single length ofconductive wire, each of which forms a plurality of spaced apart filtercomponents 324, 325, respectively. Filter components 324, 325 comprisenon-resonant filters or inductors that are spaced apart along the lengthof conductive electrode wires 322, 323. Electrodes 319, 318 are locatedon the first end 312 of elongate body 310 and are electrically coupledto the first and second conductive wires 322, 323, respectively. In theillustrated embodiment, first electrode 319 is a ring electrode andsecond electrode 318 is a tip electrode. However, the electrodes 318,319 may be any type of electrodes known to those skilled in the art oflead assemblies. For example, the electrode may be a single tipelectrode. Alternatively, the electrodes may be one or a series of ringelectrodes. Still yet alternatively, the electrodes may be electrodesplaced on either side of the housing. Thus although the illustratedembodiment is depicted as including tip and ring electrodes any of theforegoing electrodes fall within the scope of the invention.

The first and second conductive wires 322, 323 are electricallyinsulated from one another. Both the first and second conductive wires322, 323 may include an insulative or non-conductive coating. Preferablythe insulative coating is a heat bondable material such as polyurethane,nylon, polyester, polyester-amide, polyester-imide,polyester-amide-imide and combinations of the foregoing. Alternatively,only one wire may be insulated. The wire insulation comprises thebondable material mentioned previously. In addition, circuits 320, 321,as best seen in FIG. 3B, are further electrically insulated as bothelectrode wires 322, 323 are wound around non-conductive tube 330defining a lumen therewithin. Tube 330 may be formed of a siliconematerial, Teflon, expanded tetrafluoroethylene (eTFE),polytetrafluoroethylene (pTFE), or the like, as described below. Windingthe non-resonant filters 324, 325 or inductors around non-conductivetube 330 facilitates construction of the inductors and resonant LCcircuit. Moreover, non-conductive tube 330 advantageously allows thecircuits to maintain flexibility and maneuverability when placed insidean elongate body. Advantageously, other items necessary or desirablyused in the surgical or interventional procedure such as fiber opticcables, irrigation lumens, coaxial cables may also be passed through thelumen of tube 330.

Referring to FIG. 3A, ring electrode 319 is coupled to the firstconductive wire 322 with tip electrode 318 located distal to the ringelectrode 319 and coupled to the second conductive wire 323 at the firstend 312 of lead assembly 300. Lumen 316 houses circuits 320, 321comprising electrode wires 322, 323, respectively. Alternatively, and asbest illustrated in FIG. 4B, electrode wires 322, 323 may be embeddedwholly or partially in jacket 311. As discussed previously, eachelectrode wire 322, 323 forms a plurality of spaced apart filtercomponents 324, 325 comprising non-resonant filters. As in previousembodiments, each circuit is optionally constructed from a single,continuous length of non-magnetic wire such as copper, titanium,titanium alloys, tungsten, gold and combinations of the foregoing;however, each circuit may alternatively be constructed from multiplelengths of electrode or include discrete filter components connected byseparate lengths of electrode wires. If all filters are formed from onelength of wire, it is important that the wire is a bondable wire such asheat, chemical or adhesively bondable to permit formation of the filtersduring manufacture with one wire as will be described below.

Referring now to FIG. 3B is a sectional view of an exemplary medicaldevice including MR compatible conductive electrode wires in whichnon-resonant filters 324′, 325′ are formed without any gaps therebetweenand in which one electrode circuit 322′ is wound on top of or over asecond electrode circuit 323′ is depicted. Those of skill in the artwill appreciate that the two circuits are at least partially in aco-axial relationship. In this configuration, the non-resonant portionsshare the same axis. Referring to FIG. 3A the non-resonant portions ofthe two circuits as well as the resonant LC filters 326′, 327′ arepositioned along the same longitudinal axis in a parallel relationship.Those of skill in the art will appreciate that the MR CompatibleElectrode circuit may comprise any number of circuits and those circuitsmay be positioned in the elongate body along different axes. It is alsoto be appreciated by those of skill in the art the electrode circuits inaccordance with the invention may share a common axis but have differentinner diameters.

FIG. 3C is a sectional view of an exemplary medical device including MRcompatible conductive electrode wires in which one resonant LC filter326′ is wound on top of or over a second resonant LC filter 327′ in aco-axial relationship.

FIG. 3D is a sectional view of an exemplary medical device including aplurality of circuits in which the non-resonant section comprises onenon-resonant filter or alternatively a plurality of non-resonant filterswound so that no gaps are between the filters.

Referring now to FIG. 3E each circuit 320, 321 is constructedsubstantially similarly. Electrode wires 322, 323 are wound overflexible tube 330 which is preferably made from polyimide, polyolefin,pTFE, eTFE, polyetherketone (PEEK) and other similar flexible materials.During manufacture a stiff rod (not shown) is placed inside of flexibletube 330 to provide added support for the assembly process. Aftermanufacture, the rod is removed and the flexible tubing 330 with circuitconstructs is placed in elongate body 310.

Each circuit 320, 321 is constructed separately with the first circuit320 being constructed from the distal end to the proximal end startingwith the most proximal resonant LC filter 326. Thus, assuming aplurality of circuits, the electrode wire associated with the next mostdistal resonant LC filter 327 passes over the resonant LC filter that ismost proximal. Passing an electrode wire below a resonant LC filter willadversely affect its resonance. On the other hand, passing a wireunderneath a non-resonant inductor will not adversely affect itsperformance. Thus, exemplary resonant LC filter 326 is constructed bylayering of the electrode wire 322 to form three layers 335, 336, 337.The ratio of turns from inner layer to outer layer may be approximately3:2:1 resulting in a constant physical geometry of the resonant LCfilter. Creating a resonant LC filter is apparent to those skilled inthe art, and many embodiments would satisfy the requirements of thisinvention. For example, a capacitor may be placed in parallel with aninductor. Other types of resonant LC filters would also fall within thescope of the invention.

In the exemplary embodiment, multiple layers of coiled wire areconstructed such that the capacitance between the layers and individualturns provide the ratio of inductance to capacitance required to satisfythe resonant condition and provide the maximum impedance at the resonantfrequency. As described previously, three layers may be used, the ratioof turns from inner layer to outer layer being approximately 3:2:1. Thisratio results in high structural integrity, manufacturability, andrepeatability. In the exemplary embodiment, wherein the resonantfrequency of the resonant LC filter is approximately 64 MHz to block theRF from a 1.5 Tesla MRI, the inner layer may include 30 turns, themiddle layer may include 20 turns, and the outer layer may include 10turns. In general, the exact number of turns is determined by the spaceavailable and the desired resonant frequency. The impedance, bandwidthand quality factor of the resonant LC filter can be adjusted bymodifying the ratio of the capacitance to the inductance of the filter.This may be accomplished by changing the number of turns, the number oflayers, the ratio of turns between layers, or all of these. For example,the ratio may vary in each case by one, two or three turns to obtain thedesired characteristics of the filter.

After forming the most proximal resonant LC filter 326, first electrodewire 322 is helically wound around tube 330. Those of skill in the artwill appreciate that connecting segments 332 do not necessarily need tocomprise a specific numbers of turns around tube 330. Rather, it isimportant to wind the electrode wires in such a manner as to includesome slack or “play” thereby allowing the lead assembly to maintain itsflexibility during use. Inductors 324 are next formed by coilingelectrode wire 322 over flexible tube 330. Each inductor 324 may beformed by helically winding or coiling electrode wire 322 approximatelyforty-five turns, creating approximately 150 ohms, when sized to fit inan 8 French catheter assuming an inside diameter of the inductor to be0.045 inches. Those of skill in the art will appreciate, however, thatfewer turns may be necessary to create the same impedance for largerdiameter inductors. Inductors 324 may be spaced non-uniformly, such thatthe segments of wire between them each have a different resonantfrequency, or may be placed substantially uniformly.

Second circuit 321 is constructed next and substantially similarly tocircuit 320. Those of skill in the art will appreciate that theexemplary lead assembly illustrated in FIGS. 3A and 3B comprises twocircuits 320, 321 and two electrodes 319 and 318. However, any number ofcircuits and corresponding electrodes can be constructed. For example,in one exemplary construct four circuits each comprising a plurality ofnon-resonant filters and a resonant LC filter are electrically coupledto four electrodes (three ring electrodes and one tip electrode oralternatively four ring electrodes). In another exemplary construct tencircuits each comprising a plurality of non-resonant filters and aresonant LC filter are electrically coupled to ten electrodes. Anynumber of circuits can be constructed. In each case, however, thecircuit that includes the most proximal resonant LC filter isconstructed first and the circuit that includes the most distal resonantLC filter is constructed last so that the plurality of resultingelectrode wires housed within a catheter have the connecting electrodewire segments passing over all proximal resonant LC filters. Forexample, constructing circuits 320, 321 may be done by starting at theproximal end first (rather than the distal end) so long as the circuitthat includes the most proximal resonant LC filter is constructed first.In this way the connecting electrode wire segments of the subsequentlyconstructed circuits will always pass over all adjacent, proximalresonant LC filters so that resonance is not disturbed. Other assemblytechniques will be apparent to those of skill in the art.

As shown in FIGS. 4A and 4B the circuits can be constructed so that theresonant and/or non-resonant filters may be embedded, partially orwholly, in the catheter jacket.

Referring now to FIG. 5 one embodiment of the invention is shown. Inthis exemplary circuit 520, multiple, small non-resonant filters 524 aregrouped together to form a plurality of inductors 540 positioned in aspaced apart relationship along the length of conductive electrode wire522. This grouping of filters collectively increases the impedance ofeach non-resonant filter and reduces the current along the conductiveelectrode wire 522. As in other embodiments filter component at theelectrode/wire interface 528 includes resonant LC filter 526 that isadapted to effectively block RF induced current from exiting the leadassembly 500 through electrode 518. Groups 540 of non-resonant filters524 distributed along the length of electrode wire 522 attenuate theinduced current on the wire itself before the current reaches resonantLC filter 526 thereby avoiding excessive heating of resonant LC filter526. Groups 540 of non-resonant filters 524 may also attenuate the RFcurrent reflected from resonant LC filter 526 thereby attenuating thestrong reflected power from the resonant LC filter 526. The embodimentdepicted in FIG. 5 is constructed in much the same way as previouslydescribed with respect to FIG. 3B.

Referring now to FIG. 6A-FIG. 6C an alternative embodiment 600 of theinvention is shown. As can be seen in FIG. 6A two electrode wires 640,650 are provided and wound in a co-radial fashion. The co-radially woundelectrode wires 640, 650 share a common magnetic flux channel in thecenter of the windings, such that common mode RF present on both wireswill tend to cancel and thus be attenuated. This co-radial approach maybe expanded to more than two electrode wires and may comprise any numberof co-radially wound wires. Those of skill in the art will appreciatethat co-radially wound electrode wires behave as non-resonant filters.

Referring to FIG. 6B, lead assembly 600 includes elongate body 610surrounded by jacket 611. Elongate body 610 includes first 612 andsecond 614 ends and includes lumen 616 therewithin. Second end 614 isadapted to be connected to electronics, internal or external to thepatient body, and may include a connector (not shown). Lumen 616 housesco-radially wound conductive electrode wires 640, 650. In an alternativeembodiment, best shown in FIG. 6C, co-radially wound wires 640, 650 maybe embedded in jacket 611. Each co-radially wound electrode wire 640,650 comprises a single length of conductive wire thereby eliminating theneed for bonding points and reducing the possibility of mechanicalfailure of the wire. The conductive electrode wires 640, 650 are woundin the same direction and the coils have the same diameter. When thelead assembly is exposed to an RF field, as during an MRI scan, theco-radially wound electrode wires 640, 650 tend to block higherfrequency common mode RF current from being transmitted along the lengthof an individual conductive wire. Each co-radially wound conductiveelectrode wire 640, 650 may have an equal or unequal number of turns.Preferably, however, the conductive electrode wires 640, 650 include anequal number of turns to minimize the amount of RF leakage from thecoil, such leakage resulting in less effective RF current blocking. Inthe embodiment shown in FIGS. 6B and 6C, the co-radially wound wires640, 650 extend substantially along the entire length of the leadassembly, proximal to the resonant LC filter assembly. In otherembodiments (not shown) the co-radial conductive electrode wires mayextend only along a portion of the lead body.

In the exemplary coiled configuration, first and second conductive wiresare electrically insulated from one another. Both the first and secondconductive wires 640, 650 may include an insulative or non-conductivecoating. The insulative coating may be formed of a polyurethanematerial, nylon, polyester, polyester-amide, polyester-imide,polyester-amide-imide, silicone material, Teflon, expandedtetrafluoroethylene (eTFE), Polytetrafluoroethylene (pTFE), and thelike. Alternatively, only one wire may be insulated. In any case,electrode wires should be electrically isolated from each other.

As in previous embodiments, each co-radially wound electrode wire 640,650 is constructed from a single, continuous length of non-magnetic wiresuch as copper, titanium, titanium alloys, tungsten, gold andcombinations of the foregoing. If each wire electrode is constructedfrom one length of wire, it may be a bondable wire such as heat,chemical or adhesively bondable to permit formation of the filtersduring manufacture with one wire. Alternatively, several lengths ofnon-continuous wire may be used and still fall within the intended scopeof the invention. In such case the wires may be cast in silicone andheat-treated in certain location to ensure that the wire does not shift.Alternatively, glue or a wire having sufficient rigidity so that itholds its shape when bent may be used to prevent the wire comprising thecircuit from shifting.

As best seen in FIG. 6B first and second resonant LC filter assemblies626, 627 are constructed as hereinbefore described. Resonant LC filters626, 627 may be placed adjacent and proximal to the wire/electrodeinterface to effectively block RF induced current from exiting the leadassembly through the electrode. Co-radially wound wires 640, 650 actlike non-resonant filters and attenuate the induced current on the wireitself before the current reaches the resonant LC filter therebyavoiding excessive heating.

As with other embodiments, electrode wires 640, 650 are co-radiallywound over a length of flexible tubing 340 made from polyimide,polyolefin, pTFE, eTFE, polyetherketone (PEK) and other similar flexiblematerials. The choice between utilizing co-radially wound electrodewires versus discrete inductors on each electrode wire depends onseveral factors. Co-radially wound wires can be implemented in a smallerdiameter lead, since one electrode wire never needs to pass over orunder another, except at the resonant LC filters. However, the impedanceof the discrete inductor approach may be more predictable and is not asdependent on length or bend of the device.

In the various embodiments presented herein the conductor includes asufficient cross-sectional area such that the resistivity of theconductor at the MR operating frequency of 64 MHz for a 1.5 Tesla MRI islow enough to ensure that at Joule heating of the wire is minimal. Inone embodiment, the wire may be a 36 AWG copper magnet wire for acircuit that is approximately one meter in length. Numerical modelingsuch as for example Finite Difference Time Domain (FDTD) or Method ofMoments may be used to approximate the expected current for a particulardevice. The length of wire being used and the expected trajectory in thepatient determines the desired total impedance across the circuit. Thus,for any particular length of wire the appropriate gauge may then beselected.

A current of 100 mA DC will result in approximately a 10.degree. rise intemperature in a short section of coiled 40 AWG wire. For a 36 AWG wire,the temperature rise is reduced to a 2.degree. rise in temperature. ForAC, the conductor resistance increases with frequency. An increase offive fold or greater is possible when comparing the DC resistance to theresistance of 60 MHZ, which directly translates to a greater temperaturerise of the conductor for the same power input. The novel electrode wireconstruct in accordance with the present invention is configured to beintegrated into a 10 French or smaller lead assembly or catheter.

Various modifications and additions can be made to the exemplaryembodiments discussed without departing from the scope of the presentinvention. For example, while the embodiments described above refer toparticular features, the scope of this invention also includesembodiments having different combinations of features and embodimentsthat do not include all of the described features. Accordingly, thescope of the present invention is intended to embrace all suchalternatives, modifications, and variations as fall within the scope ofthe claims, together with all equivalents thereof.

What is claimed is:
 1. A lead assembly comprising: an elongate body having a proximal end and a distal end, said elongate body defining a lumen therewithin, the distal end arranged and configured to contact tissue and the proximal end operably coupled to an electronic control; a plurality of electrodes located on the elongate body; and a plurality of electrode circuits each of which is in communication with a respective one of said plurality of electrodes, said plurality of electrode circuits housed within said elongate body and each comprising one or more electrode wires, said one or more electrode wires forming one or more non-resonant filters and one or more resonant LC filters.
 2. The lead assembly of claim 1 wherein said one or more electrode wires each comprise a single continuous length of electrode wire.
 3. The lead assembly of claim 2 wherein said one or more non-resonant filters comprise a single non-resonant filter positioned along a portion of the length of the electrode circuit.
 4. The lead assembly of claim 1 wherein said one or more non-resonant filters comprise a plurality of non-resonant filters positioned in a uniform or non-uniform spaced-apart relationship along a portion of the length of the electrode circuit.
 5. The lead assembly of claim 1 wherein said at least one non-resonant filter is constructed from a length of electrode wire that is not continuous with a length of electrode wire used to construct said at least one resonant LC filter.
 6. The lead assembly of claim 1 wherein said one or more electrode wires comprises a single length of multiple non-continuous wires.
 7. The lead assembly of claim 1 wherein said one or more non-resonant filters in a single electrode circuit comprises a plurality of non-resonant filters positioned in a non-spaced apart relationship with no gaps therebetween along a portion of the length of the electrode circuit.
 8. The lead assembly of claim 1 wherein said one or more non-resonant filters comprise a plurality of non-resonant filters positioned in a co-axial relationship.
 9. The lead assembly of claim 1 wherein said one or more resonant LC filters comprise a plurality of resonant LC filters positioned in a co-axial relationship.
 10. The lead assembly of claim 1 wherein said plurality of electrode circuits share the same longitudinal axis along at least a portion thereof.
 11. The lead assembly of claim 10 wherein said plurality of electrode circuits share the same longitudinal axis in a parallel relationship to each other along at least a portion thereof.
 12. The lead assembly of claim 1 wherein said plurality of electrode circuits are positioned along different axes of the elongate body.
 13. The lead assembly of claim 1 wherein said plurality of electrode circuits share a common axis along at least a portion thereof but have different inner diameters.
 14. The lead assembly of claim 1 wherein said one or more electrode wires comprise copper, titanium, titanium alloys, tungsten, gold, multifilar and combinations of the foregoing.
 15. The lead assembly of claim 1 wherein one or more electrode wires includes an insulative coating bondable by heat, chemical or adhesive means.
 16. The lead assembly of claim 1 wherein said plurality of electrodes are positioned in a parallel relationship on either side of said elongate body.
 17. The lead assembly of claim 1 wherein said electrode circuit is housed entirely within the lumen of said elongate body.
 18. The lead assembly of claim 1 further comprising a flexible tube around which said at least one non-resonant and resonant LC filters are helically wound.
 19. The lead assembly of claim 1 wherein said one or more resonant LC filters comprise a plurality of physically stacked layers.
 20. The lead assembly of claim 19 wherein said physically stacked layers comprise an inner layer, a middle layer and an outer layer.
 21. The lead assembly of claim 20 wherein said inner layer, middle layer and outer layer are formed from said one or more electrode wires in a ratio of turns of approximately 3:2:1.
 22. The lead assembly of claim 21 wherein said inner layer is constructed of approximately 30 turns, said middle layer is constructed of approximately 20 turns, and said outer layer is constructed of approximately 10 turns of said one or more electrode wires.
 23. The lead assembly of claim 1 wherein said one or more non-resonant filters are configured to create at least 1,000 or more Ohms of impedance along said electrode circuit for each one meter of lead assembly length.
 24. The lead assembly of claim 1 wherein the circuit is flexible.
 25. The lead assembly of claim 1 wherein the circuit is rigid.
 26. The lead assembly of claim 1 wherein said one or more non-resonant filters and said one or more resonant LC filters comprise discrete filters structured to be joined by multiple connecting segments of electrode wire.
 27. The lead assembly of claim 4 wherein said uniform spacing comprises repetitious spacing.
 28. The lead assembly of claim 1 wherein said one or more electrode wires comprise copper, titanium, titanium alloys, tungsten, gold, multifilar and combinations of the foregoing.
 29. The lead assembly of claim 1 wherein said one or more electrical circuits are housed entirely within the lumen of said elongate body.
 30. A lead assembly comprising: an elongate body having a proximal end and a distal end, said elongate body defining a lumen therewithin, the distal end arranged and configured to contact tissue and the proximal end operably coupled to an electronic control; one or more electrodes located on the elongate body; and one or more electrical circuits each of which is in communication with a respective said one or more electrodes, each of said one or more circuits housed within said elongate body and comprising one or more electrode wires, said one or more electrode wires forming at least one non-resonant filter having a substantially uniformly distributed inductance along the length of said electrode wire and at least one resonant LC filter.
 31. The lead assembly of claim 30 wherein said at least one non-resonant filter comprises a plurality of non-resonant filters positioned in a spaced apart relationship along a length of said electrical circuit.
 32. The lead assembly of claim 31 wherein said spaced apart relationship is repetitious.
 33. The lead assembly of claim 31 wherein said spaced apart relationship is uniform.
 34. The lead assembly of claim 30 wherein said one or more wires each comprise a single, continuous length of electrode wire forming said at least one non-resonant filter and said at least one resonant LC filter.
 35. The lead assembly of claim 30 wherein said one or more non-resonant filters comprise a single non-resonant filter positioned along a portion of the length of the electrode circuit.
 36. The lead assembly of claim 30 wherein said at least one non-resonant filter is constructed from a length of electrode wire that is not continuous with a length of electrode wire used to construct said at least one resonant LC filter.
 37. The lead assembly of claim 30 wherein said one or more non-resonant filters in a single electrode circuit comprises a plurality of non-resonant filters positioned in a non-spaced apart relationship with no gaps therebetween along a portion of the length of the electrode circuit.
 38. The lead assembly of claim 30 wherein said at least one non-resonant filter comprises a plurality of non-resonant filters positioned in a co-axial relationship.
 39. The lead assembly of claim 30 wherein said at least one resonant LC filter comprises a plurality of resonant LC filters positioned in a co-axial relationship.
 40. The lead assembly of claim 30 wherein said one or more electrical circuits comprise a plurality of electrode circuits that share the same longitudinal axis along at least a portion thereof.
 41. The lead assembly of claim 40 wherein said plurality of electrical circuits share the same longitudinal axis in a parallel relationship to each other along at least a portion thereof.
 42. The lead assembly of claim 30 wherein said one or more electrical circuits comprise a plurality of electrical circuits positioned along different axes of the elongate body.
 43. The lead assembly of claim 30 wherein said one or more electrical circuits comprise a plurality of electrical circuits that share a common axis along at least a portion thereof but have different inner diameters.
 44. The lead assembly of claim 30 wherein said one or more electrode wires include an insulative coating bondable by heat, chemical or adhesive means.
 45. The lead assembly of claim 30 wherein said one or more electrodes are positioned in a parallel relationship on either side of said elongate body.
 46. The lead assembly of claim 30 further comprising a flexible tube around which said at least one non-resonant and resonant LC filters are helically wound.
 47. The lead assembly of claim 30 wherein said one or more resonant LC filters comprise a plurality of physically stacked layers.
 48. The lead assembly of claim 30 wherein one or more of said electrical circuits are flexible.
 49. The lead assembly of claim 30 wherein one or more of said electrical circuits are rigid.
 50. The lead assembly of claim 30 wherein said at least one non-resonant filter and said at least one resonant LC filters comprise discrete filters structured to be joined by multiple connecting segments of electrode wire. 